Hammer drills are power tools that generally have three modes of operation, i.e. a hammer only mode, a drill only mode and a combined hammer and drilling mode. In general, the motor of a hammer drill is operated by the user depressing a spring-loaded trigger, and deactivated by the user releasing the trigger such that it is necessary to hold the trigger down during operation of the tool.
UK patent no. 2314288 describes an electric combination hammer having a drilling mode and a chiselling mode. The hammer comprises a housing with a handle and a trigger disposed on the handle for operating an electric on/off switch. The combination hammer has an operating knob for switching manually between the drilling mode and the chiselling mode, and the trigger has an associated detent which, when the operating knob is in the position corresponding to the chiselling mode, allows the on/off switch to be latched in a closed position such that even when the user releases their grip on the trigger the combination hammer remains in operation.
The electric combination hammer of GB2314288 suffers from the drawback that the components for the detent system are mechanical in nature, comprising cam surfaces and resilient springs, such that they are susceptible to wear and tear with repeated use. Also, the use of such mechanical components makes the hammer expensive to manufacture.
Preferred embodiments of the present invention seek to overcome the above disadvantage of the prior art.